The invention relates generally to a measuring system for measuring any number of physical parameters and more particularly to a modular metering instrument having a meter module to which can be attached a variety of detachable sensing probes.
A plurality of physical parameters, such as fluid temperature, velocity, pressure, volume flow and humidity can be measured with a conventional meter and the appropriate sensing probes. In the prior art systems and techniques, each time a parameter was to be measured, a new design for an entire metering system including the sensor or sensing probe was required. These techniques are both cumbersome and inefficient.
The utilization of multiple probes with a common meter is not common in measurements such as thermal anemometry, since it is very difficult to obtain acceptable calibration accuracy. Generally it is very difficult to manufacture such sensing probes exactly alike, therefore the calibration curve of each probe is significantly different.
One technique to achieve the utilization of multiple probes with a common meter is to manufacture the probes with great care so that the probes essentially are identical. With such a technique, a common field practice is then to utilize multiple scales for analog instruments or large calibration look up tables for digital instruments. If the probes are not closely matched during manufacture, such calibration tables will be significantly different between probes. The prior systems store the large calibration tables in the meter electronics. This technique complicates the utilization of multiple probes.
It thus would be desirable to provide a modular metering instrument adapted to be attached to a variety of sensing probes, which probes are not manufactured exactly alike without affecting the calibration of the modular metering instrument.